X-ray tube.



F. A. WIGGIN.

X-RAY TUBE.

APPLICATION FILED OCT. 5, WW.

1,218,026. I Patented Mar. 6,1917

FRED A. wreem, or LAWRENCE, MASSACHUSETTS.

x-EAY TUBE.

Specification of Letters Patent.

Patented Mar. 6, 1917.

Application filed October 5, 1916. Serial m5. 123,943.

tion, like letters on the drawings representing like parts.

My present invention relates to improvements in targets for X-ray tubes and the object of the invention is to improve and perfect X-ray targets, and especially to enable them to better withstand higher powered apparatus than those now in use; and it is also an object to devise a simple process of constructing such targets. a

In the use of an X-ray tube the-heat generated by the cathode stream raises the temperature of the target so rapidly that unless it were immediately diffused and conducted away, the receiving surface of the target would be fused, even if made of a most refractory metal, and it has heretofore been very diificult to provide an eflicient and satisfactory target and maintain its radiating surface against the cathode stream of the electric current focused on the target. Such target must have a refractory face to withstand the intense heat there developed, which face must'be connected by a perfect mechanical, physical, electrical and thermal contact to a good heat conductor of suflicient mass to carry away from the radiating surface the heat as developed, so as to prevent the surface from actually becoming fused by the heat and pierced by the cathode stream focused thereon. To meet the exacting conditions of such work, platinum or metals of the latinum group have been used for the r'eflectmg surface and a copper backing has been welded or fused onto the platinum surface for heat conduction, actually forming the two materials into anintegral structure and in the absence of any extraneous uniting substance. Such a plate thus formed might then be united in any de-- sired manner to a further backing substance. Such a construction is shown by U. S. Patent No. 1,002,390, issued Sept. 5, 1911, but it has been found that such platinum targets would not standup for long orpractical use with high powered apparatus. Subsequent to the issue of said patent, efforts were made to use tungsten as the refractory material for the surface of the targets, unitin' 1t in direct mechanical, physical and therma contact with a copper backing.- Although tungsten had been well known as a highly refractory material, yet it had never been actually utilized for 'X-ray tubes until recently, owing to the extreme difliculty of handling and working this material.

In the case of attaching tungsten directly to a copper backing, however, the difference in the co-efiicients of expansion between the two metals inthe intense heat of an X-ray target caused the tungsten to separate from the copper and drop away from it entirely, thus eliminating the heat-conducting function of the copper and destroying the efliciency of the X-ray tube. Furthermore, tungsten could not be united tooa silver backing or the like which had such a low melting point in comparison to tungsten that, under the heat generated in use in targets, not only would the tungsten drop off, but the volatilized silver would blacken upthe X-ray tube and destroy the .efliciency of the entire apparatus, and repeated experiments along these lines failed to'produce a satisfactory commercial article.

As tungsten is a very expensive -material, besides being diflicult to work, it is desirable, if possible, to utilize a small amount of tungsten for the surface, rather than to make the target entirely of tungsten. I

I have discovered that by using tungsten, preferably as a small button-or insert for the reflecting surface of the center of the v target, fitting the same into a corresponding recess in a suitable backing material, such as copper, and covering the back and sides of the tungsten button with a metal capable of a degree of expansion intermediatethat of tungsten and copper and of a fusion point intermediate that of tungsten and copl per, a construction is obtained whereby there is a suitable give and take to prevent separation of the several metals. Such an'intermediate metal must also be capable of firmly unifying the tungsten and copper to obtain the advantages of the heat conduction so necessary. For this intermediate substance I find that a metal, such as nickel, iron, Monelmetal, or their equivalents, is preferable, each one named fulfilling these demands in all ways: Furthermore, this construction permits a relatively simple method of building such a composite target and eliminates thelnecessity for the expensive and difficult process heretofore necessary where the tungsten itself was fused or welded direct to the copper back.

In carrying out my invention I may providethe tungsten button with a covering at 'the copper surface or both if desired. While any suitable method of applying such intermediate metal may be employed, I find that it is feasible, in the use of nickel, for

example, to plate a coating directly on the back and sides of the tungsten button. While I prefer to make this target with a button construction covered both on the back and sides, and insert the same in a recess in the copper backing, it is, of course,

feasible to similarly attach a plate on the copper backing without inserting it therein. I have found that this construction produces a target which will permit the use of a cathode stream of higher intensity, without separation of the receiving and conducting metals, than is possible with any existing composite target.

Referring to the drawings illustrating my improved target construction,

Figure 1 is a diagrammatic view, partly in cross-section, of the X-ray tube; Fig. 2 is an enlarged cross-sectional view showing the button construction; and

Fig. 3 is a similar view in cross-section illustrating the plate construction.

Referring to the drawings, an X-ray tube of standard construction. is designated at A, having the ,two customary terminals therein, comprising the cathode B and the target C, the target being of .usual form. The target C comprises a mass of copper O, constituting the backing and support for the face D, which, as shown in Fig. 2, is a thin button of tungsten with its intermediate binding metal E, set in a suitable recess X, formed within thebacking C and preferably of appropriate depth to enable the surface of the tungsten D to be flush with the face -K of theportion C,

thus constituting a target having a substantially perfect thermal connection from the target surface D on which the rays are focused to the copper backing C.

In Fig. 3 I have illustrated the invention in a modified form having the copper backing H and the tungsten plate F united directly thereto by the intermediate binding metal G.

It will be appreciated that a relatively thin covering of the intermediate metal will operate in the several capacities of uniting and binding the tungsten and copper in the necessary firm and thermal contact for heat conductivity, while also affording the necessary medium to allow for the give and take or resiliency demanded by the differences in the expansion of the tungsten surface and copper backing.

While I have referred to tungsten, it will be understood that I may use tungsten or any of its alloys, platinum, iridium, tantalum, or other metals of the platinum group and its alloys, and While I have also referred to the member C as of copper, it will be understood that an equivalent metal may be substituted therefor, or bronze, copper composition, or the like, such backing being usually now made of copper because of its electrical and heat conductive qualities and reasonableness in price for this purpose. 7

My invention is further described and defined in the form of claims as follows:

1. An X-ray target, comprising a face of highly refractory metal, a backing metal of relatively high heat conductivity, and an intermediate metal or alloy having a co-efficient of expansion intermediate that of the refractory metal and said backing.

2. An X-ray target, comprising a face plate of highly refractory metal, a backing metal of relatively high heat conductivity,

and an intermediate metal or alloy having a co-efiicient of expansion intermediate that of the refractory metal and said backing, said intermediate metal constituting a binding medium between the refractory metal and said backing and being of sufficient extent to allow for the difierences in expansion of the said refractory metal and said backing during use.

3. An X-ray target comprising a face plate of tungsten, a backing metal of relatively high heat conductivity, and an intermediate metal or alloy having a co-eflicient of expansion intermediate that of the tungsten and said backing.

4. An X-ray target comprising a face plate of tungsten, a backing metal of relatively high ,heat conductivity, and an intermediate metal or alloy having a co-efiicient of expansion intermediate that of the tungsten and said backing, said intermediate metal constituting a binding medium between the tungsten and said backing and being of sufficient extent to allow for the differences in expansion of the tungsten and said backing during use.

5. An X-ray target comprising. a face plate of tungsten alloy, a backing metal of relatively high heat conductivity, and an intermediate metal or allQy having a co-eficient of expansion intermediate that of the tungsten alloy and said backing.

6. An X-ray target comprising a face of highly refractory metal, a backing metal of relatively high heat conductivity, and an intermediate binder of nickel, having a co-eflicient of expansion less than that of copper and greater than that of the refractory metal.

7. An X-ray target comprising a face of tungsten, a backing metal of relatively high heat conductivity, and an intermediate than that of tungsten.

8. An X-ray target, having a faceof highly refractory metal, a backing metal ofv relatively high heat conductivity, and an intermediate metallic substance having its fusion point and co-eflicient of expansion intermediate that of the refractory-metal and said backing.

In testimony whereof, I have signed my name to this specification, in the presence of two subscribing witnesses.

FRED A. WIGGIN.

Witnesses:

JAMES R. HODDER, HAROLD J. CLARK. 

